This invention relates to a method for manufacturing credit cards and the like, containing a microprocessor chip, as well as to credit cards and the like produced in accordance with the said manufacturing method.
These cards which have been devised recently are mainly credit cards containing an electronic module using a highly performing electronic component known as an electronic chip.
The main problem arising in the design of such "chip cards" relates to the positioning and fixation of the electronic module in the plastic card.
At present, most chip cards are manufactured by cutting out at first the plastic card from a board or by molding this card from plastic material.
This plastic card is shaped with a recess within which the electronic module will be positioned and glued in place.
The document EP 0 254 640 describes a method of this kind for producing chip cards. In this document, there is provided, according to a first embodiment, the formation of a cavity which opens into both faces of the plastic card, the electronic module being then positioned with its contact pieces flush with one face of the card, and the cavity being thereafter filled with glue for fixing said module. The module will then be protected to some extent by the glue, but there remains a risk that it may be subjected to external strains liable to impair its reliability.
In order to obtain a better protection of the electronic module, a second embodiment consists in forming a recess which opens into only one face of the card. The module will then not be accessible through the back of the card. However, this embodiment requires very complex operations, because every dimension must be strictly respected, since otherwise this would produce a card in which the contacts would not lie in the plane of the plastic card.
In order to overcome these drawbacks, it has been attempted to produce a chip card by molding the card body around the electronic module. For this purpose, the electronic module is positioned in a mold into which will be injected the plastic material for forming the plastic card.
A method of this kind is described, for instance, in the Japanese document 59.73567 or in the European document 0 227 854.
These methods are not satisfactory because they do not completely ensure that the positioning of the electronic module in the mold will be safely preserved.
The Japanese document provides for positioning the module by inserting into a recess of the mold a tenon carried by the module. Using this method, it is not possible to achieve a good quality of the card, because the plastic material being injected at a pressure of about
700 kg/cm.sup.2 displaces the module.
European Patent 0 277 854 attempts to improve this method by using a vacuum system for holding down the module during the plastic injection. This suction is moreover provided for holding down the contacts of the module against the internal face of the mold.
This arrangement is not very effective, since it is difficult to obtain by means of a vacuum pump that the module will be maintained in place against the pressure exerted by the plastic material being injected.
This European Patent provides a second arrangement in which the electronic module is maintained by a plate supported by springs. In this arrangement, it is provided that during the molding process the plastic will first surround the module before pushing down the said plate against the springs in order to completely fill the cavity of the mold.
This is completely unrealistic, since the pressurized plastic will act upon the plate from the very start of the injection process, so that the module will no longer be kept in place. These arrangements do not make it possible to obtain cards in which the module is perfectly positioned and, moreover, the plastic seeps in between the contacts and the wall of the mold, thus soiling the contacts and making it necessary to provide a cleaning operation for cleaning these contacts. Obviously, this cleaning adds considerably to the production cost of the card.
The module described and used in this Patent is formed from a board of insulating material, one face of which receives a metal overlay for forming the contacts.
On the opposite face, the electronic chip will be fixed and wired, and then coated with resin. A module of this type is difficult to use because the resin does not adhere properly to the insulating material board. Also, the plastic used for forming the card body does not adhere properly to the board.
As a result, if a chip card made with such a module becomes folded, the insulating material board is separated from the plastic card and even from the resin, so that the card becomes completely unusable.
On another hand it is also stated, in this same European Patent 0 277 854, that for obtaining a proper anchoring of the module in the molded plastic, the resin coating must be given a dovetail shape. It has however been found that this disposition is very unfavorable. In fact, this dovetail shape defines a wedge-shaped volume into which the plastic material will flow during the injection process; due to the high injection pressure, the plastic material will then exert forces tending to separate the metal strip from the assembly formed of the electronic component and its coating. It is then impossible to rely, as in EP 0 277 854, on the shape given to the resin coating for fastening the module in the plastic card, and it is indeed preferable to avoid giving to the resin coating the shape described in this Patent, and much rather to give it an inverted shape, so that the forces exerted on the resin coating by the plastic material injected at a high pressure may tend to press this coating against the metal strip.
The present invention aims at overcoming these various drawbacks by providing a manufacturing method by which chip cards may be produced at a production cost which is considerably less than the present cost, and by which perfect cards may be obtained.